In manufacturing dimensionally stable sections, in particular hollow window sections, it is desirable, when producing the sections, simultaneously to mould on said layers, in order to avoid subsequent cementing operations and aftertreatments. It has been attempted to produce such dimensionally stable hollow sections with said layers in a single operation by co-extrusion. To this end protective layers or devices or the sealing and/or damping devices were extruded directly in the extrusion nozzle region, after finally forming a dimensionally stable section, through additional nozzle channels in the region of the nozzle lip. These nozzle channels were connected to a further extruder for a plastics material which, after cooling, was soft and capable of elastic deformation. Simutaneous extrusion of the protective layers or devices, however, impedes the calibration of the dimensionally stable hollow sections and, thus increases the production costs.
EP-A-159 307 concerns the application to a tubular hollow section, for example a cable conduit, of an electrically conductive wire or a tape. The wire or the conductive tape is, however, produced in a separate operation, prior to being applied to the cable conduit. It has been proposed to heat said wire or the tape after the hollow section or cable conduit has cooled to a temperature of 50.degree. C., that is to say to a dimensionally stable state in that region in which the wire or tape is to be attached to the periphery of the cable conduit. The wire or the tape which is to be applied is heated by means of a heat source and pressed, by means of a pressure device which may, if required, be heated, onto the surface of the cable conduit which is moved past the pressure device in the direction of extrusion. After the application of the wire or the tape, the entire section is gripped by a crawler-type take-up for removing the extruded cable conduit. The connection between the electrically conductive wire or tape and the cable conduit is achieved by intensive heating, for example by means of gas flames or a beam of infra-red light or similar means so that, when said wire or tape is pressed under high pressure it is embedded, by virtue of local melting of the thermoplastic material of the hollow section or cable conduit, into the latter and, after cooling is fritted into the wall of the hollow section or conduit. Since in certain cases the thermal capacity of the wire is insufficient adequately to bring about embedding or fritting in position, of the wire, it has already been proposed to heat the hollow section or cable conduit in that region, where the wire or tape is to be worked in. Additionally the tubular section or the tape or the wire can be coated with a heat-responsive adhesive so that the wire or tape is not only embedded and fused in position but is also cemented to the tubular section.